Isothermal and Nonisothermal Creep of Lightly Crosslinked cis-1,4-Polybutadiene

1977 ◽  
Vol 50 (5) ◽  
pp. 884-894
Author(s):  
J. M. Caruthers ◽  
R. E. Cohen
Keyword(s):  
Activation Energy ◽  
Large Deformations ◽  
Creep Data ◽  
Creep Experiment ◽  
Viscoelastic Creep ◽  
Temperature Superposition ◽  
Linear Viscoelastic ◽  
Nonisothermal Method ◽  
Nonisothermal Creep ◽  
Good Agreement

Abstract A nonisothermal creep experiment has been analyzed to ascertain its suitability for determining the temperature dependence of low-activation-energy viscoelastic processes in elastomers far above Tg. The nonisothermal method was employed to determine the activation energy for creep near 35°C in a lightly crosslinkedcis-1,4-polybutadiene elastomer at small strains within the linear viscoelastic region and at various large deformations up to rupture. The observed activation energy was essentially independent of the level of strain, and the value of ΔHa (∼ 11 kcal/mol) determined via the nonisothermal creep method was in good agreement with the result (∼12 kcal/mol) obtained via time-temperature superposition of isothermal linear viscoelastic creep data. The nonisothermal data allowed for an estimate of the volume of the “flow unit” associated with the controlling viscoelastic creep mechanism, attributed here to slippage of entanglements within lightly crosslinked network.

Linear Viscoelastic Creep Model for the Contact of Nominal Flat Surfaces Based on Fractal Geometry: Standard Linear Solid (SLS) Material

2007 ◽  
Vol 129 (3) ◽  
pp. 461-466 ◽  
Author(s):  
Osama M. Abuzeid ◽  
Peter Eberhard
Keyword(s):  
Constitutive Law ◽  
Creep Model ◽  
Viscoelastic Creep ◽  
Flat Surfaces ◽  
Proposed Model ◽  
Linear Viscoelastic ◽  
Standard Linear Solid ◽  
Standard Linear ◽  
Creep Force ◽  
Good Agreement

The objective of this study is to construct a continuous mathematical model that describes the frictionless contact between a nominally flat (rough) viscoelastic punch and a perfectly rigid foundation. The material’s behavior is modeled by assuming a complex viscoelastic constitutive law, the standard linear solid (SLS) law. The model aims at studying the normal compliance (approach) of the punch surface, which will be assumed to be quasistatic, as a function of the applied creep load. The roughness of the punch surface is assumed to be fractal in nature. The Cantor set theory is utilized to model the roughness of the punch surface. An asymptotic power law is obtained, which associates the creep force applied and the approach of the fractal punch surface. This law is only valid if the approach is of the size of the surface roughness. The proposed model admits an analytical solution for the case when the deformation is linear viscoelastic. The modified analytical model shows a good agreement with experimental results available in the literature.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

1960 ◽  
Vol 33 (2) ◽  
pp. 335-341
Author(s):  
Walter Scheele ◽  
Karl-Heinz Hillmer
Keyword(s):  
Activation Energy ◽  
Physical Properties ◽  
Chemical Kinetics ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Limiting Value ◽  
Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

scholarly journals Drying characteristics and kinetics of fluidized bed dried potato

2008 ◽  
Vol 19 (2) ◽  
pp. 127 ◽  
Author(s):  
S.B. BAKAL ◽  
K.H. GEDAM ◽  
G.P. SHARMA
Keyword(s):  
Activation Energy ◽  
Developed Countries ◽  
Moisture Diffusivity ◽  
Drying Characteristics ◽  
Effective Moisture ◽  
Air Temperatures ◽  
Processed Products ◽  
Drying Conditions ◽  
Kinetics Of ◽  
Good Agreement

In developed countries, more than 50% potatoes are consumed as processed products. As drying is the vital phenomenon in processing, it is necessary to investigate the drying characteristics and its kinetics. In this experimental study, drying kinetics of Potato in two different shape of cuboidal & cylindrical with three aspect ratio was investigated as a function of drying conditions. Experiments were conducted using air temperatures of 50, 60 and 70 ºC, at velocity of 7 ms-1. The experimental moisture data were fitted to Page and simple models available in the literature, and a good agreement was observed. The Page model gave better fit than simple model. In the ranges covered, the values of the effective moisture diffusivity, Deff were obtained between 2.278 × 10-9 to 3.314 × 10-8 m2s-1 from the Fick's diffusion model. Using Deff, the value of activation energy (Ea) was determined assuming the Arrhenius-type temperature relationship.

Insect blood-brain barrier: a radioisotope study of the kinetics of exchange of a liposoluble molecule (n-butanol)

1976 ◽  
Vol 64 (1) ◽  
pp. 119-130
Author(s):  
M. V. Thomas
Keyword(s):  
Activation Energy ◽  
Temperature Sensitivity ◽  
Nerve Cord ◽  
Previous Investigation ◽  
Time Course ◽  
Kcal Mole ◽  
Similar Time ◽  
Kinetics Of ◽  
Butanol Concentration ◽  
Good Agreement

About 90% of the butanol uptake by the cockroach abdominal nerve cord washed out with half-times of a few seconds, in good agreement with an electrophysiological estimate, and the temperature sensitivity suggested an activation energy of 3 Kcal mole-1. The remaining activity washed out far more slowly, with a similar time course to that observed in a previous investigation which had not detected the fast fraction. Its size was similar to the non-volatile uptake, and was considerably affected by the butanol concentration and incubation period. It apparently consisted of butanol metabolites, which could be detected by chromatography.

Concerning a Creep Surface Derived From a Multiple Integral Representation for 304 Stainless Steel Under Combined Tension and Torsion

1978 ◽  
Vol 45 (4) ◽  
pp. 773-779 ◽  
Author(s):  
R. Mark ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Creep Rate ◽  
Integral Representation ◽  
Power Function ◽  
Multiple Integral ◽  
304 Stainless Steel ◽  
Creep Data ◽  
Creep Tests ◽  
Third Order ◽  
Good Agreement

It is shown that a creep surface, defined in terms of a prescribed creep rate, can be determined from the multiple integral formulation representing the creep data. The creep surface for 304 stainless steel was found to be in good agreement with a Mises ellipse. Observed creep rate vectors for this alloy were found to be normal to a Mises ellipse. These results were obtained from creep tests performed on 304 stainless steel under combined tension and torsion at 593°C (1100°F). Creep strains observed for at least 100 hr were adequately represented by a power function of time, the exponent of which was independent of stress. A third-order multiple integral representation together with a limiting stress below which creep does not occur was employed to describe satisfactorily the constant stress creep data.

Modeling of Non-Isothermal Austenite Formation in Cr5 Roller Steel

2013 ◽  
Vol 712-715 ◽  
pp. 34-37
Author(s):  
Fang Zhang
Keyword(s):  
Activation Energy ◽  
Heating Rate ◽  
Continuous Heating ◽  
Austenite Formation ◽  
Transformation Kinetics ◽  
Isothermal Heating ◽  
Critical Temperatures ◽  
Modified Model ◽  
Logarithmic Relationship ◽  
Good Agreement

A modified model describing the austenite reaction was developed that took into account the effect of heating rate. The model considered the variation of activation energy during non-isothermal heating and one set of model parameter was adequate to predict the formation of austenite. To verify the theoretical model, the process of austenite formation during continuous heating in Cr5 roller steel with pearlite and ferrite mixed initial microstructure was analyzed by dilatation experiment. The results show that a strong logarithmic relationship between apparent activation energy and heating rate. Experimental kinetic transformations as well as critical temperatures of austenite reaction are in good agreement with the calculations. The model can be used to describe the transformation kinetics at an intermediate heating rate.

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